1. Field of the Invention
The invention pertains to the field of pivoting lifters. More particularly, the invention pertains to a control system for pivoting lifters using valves to recirculate oil.
2. Description of Related Art
Conventionally, variable lift systems require oil pressure from the engine to disengage a pin on the lifter. This added oil requirement means that the oil pump must be upsized for the short periods of time that the lifter is switched. The upsized pump adds to the parasitic loss of the engine and can increase fuel consumption.
Prior art U.S. Pat. No. 6,357,406, hereby incorporated by reference, teaches a method of controlling the oil into and out of two solenoid valves controlling the two sides of the lifter plate.
U.S. Pat. No. 6,257,183 discloses a lost motion valve actuation system where a trigger valve acts as an on/off valve in directing fluid to an accumulator. The accumulator is directly hydraulically connected to the on/off valve as well as passages leading to and from the exhaust and intake tappets. Check valves are placed in the passages between the trigger valves and the tappets, permitting flow from the tappets to the trigger valve. The accumulator comprises a spring biasing means for urging a piston in a direction to decrease the size of the chamber in the accumulator. The accumulator provides surge volume and source of makeup oil and pressure to the lost motion valve actuation system. The lost motion valve actuation system does not allow proportional control of the flow of fluid and fluid is not recirculated through the on/off valve but comes directly out of the accumulator. FIG. 1 shows a graph of valve lift versus crank angle. As shown in the graph the lost motion valve actuation system changes the cam lift profile.
JP61093216A discloses a check valve that feeds oil into the pressure chambers of a tappet, which is forcibly closed by a solenoid valve. The solenoid valve is controlled by a controller in accordance with engine conditions.
JP62126213A provides oil from a remote location to communicate with an oil chamber adjacent to the tappet holder through a check valve.
JP62203911 discloses a solenoid valve that supplies working fluid to a chamber via a check valve during high loaded engine operations. The working fluid form the chamber lifts a control rod against a spring force to set valve timing.